Ultraviolet (UV) is an electromagnetic radiation with a wavelength
from 100 nm to 400 nm, shorter than that of visible light
but longer than X-rays. UV radiation is present in sunlight
constituting about 10% of the total light output of the Sun. It is
also produced by electric arcs and specialized lights, such as
mercury-vapor lamps, tanning lamps, and black lights. Although
long-wavelength ultraviolet is not considered an ionizing radiation
because its photons lack the energy to ionize atoms, it can cause
chemical reactions and causes many substances to glow or fluoresce.
Consequently, the chemical and biological effects of UV are greater
than simple heating effects, and many practical applications of UV
radiation derive from its interactions with organic molecules.
Suntan and sunburn are familiar effects of over-exposure of the skin
to UV, along with higher risk of skin cancer. Living things on dry
land would be severely damaged by ultraviolet radiation from the Sun
if most of it were not filtered out by the Earth's atmosphere.
More-energetic, shorter-wavelength "extreme" UV below 121 nm
ionizes air so strongly that it is absorbed before it reaches the
Ultraviolet is also responsible for the formation of
bone-strengthening vitamin D in most land vertebrates, including
humans. The UV spectrum thus has effects both beneficial and
harmful to human health.
Ultraviolet rays are invisible to most humans, although insects,
birds, and some mammals can see near-UV.
4 Solar ultraviolet
5 Blockers and absorbers
6 Artificial sources
6.1 "Black lights"
6.2 Short-wave ultraviolet lamps
6.3 Halogen Lamps
6.4 Gas-discharge lamps
6.7 Tunable vacuum ultraviolet (VUV) via sum and difference frequency
6.8 Plasma and synchrotron sources of extreme UV
7 Human health-related effects
7.1 Beneficial effects
7.1.1 Vitamin D
7.1.2 Skin conditions
7.1.3 Cardiovascular and hypertension
7.2 Harmful effects
7.2.1 Skin damage
Sunscreen safety debate
7.2.2 Aggravation of certain skin conditions
7.2.3 Eye damage
8 Degradation of polymers, pigments and dyes
9.2 Electrical and electronics industry
9.3 Fluorescent dye uses
9.4 Analytic uses
9.4.2 Enhancing contrast of ink
9.4.3 Sanitary compliance
9.5 Material science uses
9.5.1 Fire detection
9.6 Biology-related uses
9.6.1 Air purification
9.6.2 Sterilization and disinfection
10 Evolutionary significance
11 See also
13 Further reading
14 External links
Ultraviolet rays are invisible to most humans:- the lens in a human
eye ordinarily filters out UVB frequencies (≤ 315 nm) or
higher, and humans lack color receptor adaptations for ultraviolet
rays. Under some conditions, children and young adults can see
ultraviolet down to wavelengths of about 310 nm, and people with
aphakia (missing lens) or replacement lens can also see some UV
wavelengths. Near-UV radiation is visible to insects, some
mammals, and birds. Small birds have a fourth color receptor for
ultraviolet rays; this gives birds "true" UV vision.
"Ultraviolet" means "beyond violet" (from
Latin ultra, "beyond"),
violet being the color of the highest frequencies of visible light.
Ultraviolet has a higher frequency than violet light.
UV radiation was discovered in 1801 when the German physicist Johann
Wilhelm Ritter observed that invisible rays just beyond the violet end
of the visible spectrum darkened silver chloride-soaked paper more
quickly than violet light itself. He called them "oxidizing rays" to
emphasize chemical reactivity and to distinguish them from "heat
rays", discovered the previous year at the other end of the visible
spectrum. The simpler term "chemical rays" was adopted shortly
thereafter, and it remained popular throughout the 19th century,
although there were those who held that these were an entirely
different sort of radiation from light (notably John William Draper,
who named them "tithonic rays"). The terms chemical rays and
heat rays were eventually dropped in favor of ultraviolet and infrared
radiation, respectively. In 1878 the sterilizing effect of
short-wavelength light by killing bacteria was discovered. By 1903 it
was known the most effective wavelengths were around 250 nm. In
1960, the effect of ultraviolet radiation on
DNA was established.
The discovery of the ultraviolet radiation with wavelengths below
200 nm, named "vacuum ultraviolet" because it is strongly
absorbed by the air, was made in 1893 by the German physicist Victor
The electromagnetic spectrum of ultraviolet radiation (UVR), defined
most broadly as 10–400 nanometers, can be subdivided into a
number of ranges recommended by the
ISO standard ISO-21348:
Photon energy (eV, aJ)
Notes / alternative names
Long-wave, black light, not absorbed by the ozone layer
Medium-wave, mostly absorbed by the ozone layer
Short-wave, germicidal, completely absorbed by the ozone layer and
Visible to birds, insects and fish
Spectral line at 121.6 nm, 10.20 eV.
Ionizing radiation at
Strongly absorbed by atmospheric oxygen, though 150–200 nm
wavelengths can propagate through nitrogen
Entirely ionizing radiation by some definitions; completely absorbed
by the atmosphere
A variety of solid-state and vacuum devices have been explored for use
in different parts of the UV spectrum. Many approaches seek to adapt
visible light-sensing devices, but these can suffer from unwanted
response to visible light and various instabilities.
be detected by suitable photodiodes and photocathodes, which can be
tailored to be sensitive to different parts of the UV spectrum.
Sensitive ultraviolet photomultipliers are available. Spectrometers
and radiometers are made for measurement of UV radiation. Silicon
detectors are used across the spectrum.
People cannot perceive UV directly, since the lens of the human eye
blocks most radiation in the wavelength range of 300–400 nm;
shorter wavelengths are blocked by the cornea. Nevertheless, the
photoreceptors of the retina are sensitive to near-UV, and people
lacking a lens (a condition known as aphakia) perceive near-UV as
whitish-blue or whitish-violet.
Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly
absorbed by molecular oxygen in the air, though the longer wavelengths
of about 150–200 nm can propagate through nitrogen. Scientific
instruments can therefore utilize this spectral range by operating in
an oxygen-free atmosphere (commonly pure nitrogen), without the need
for costly vacuum chambers. Significant examples include 193 nm
photolithography equipment (for semiconductor manufacturing) and
circular dichroism spectrometers.
Technology for VUV instrumentation was largely driven by solar
astronomy for many decades. While optics can be used to remove
unwanted visible light that contaminates the VUV, in general,
detectors can be limited by their response to non-VUV radiation, and
the development of "solar-blind" devices has been an important area of
research. Wide-gap solid-state devices or vacuum devices with
high-cutoff photocathodes can be attractive compared to silicon
Extreme UV (EUV or sometimes XUV) is characterized by a transition in
the physics of interaction with matter. Wavelengths longer than about
30 nm interact mainly with the outer valence electrons of atoms,
while wavelengths shorter than that interact mainly with inner-shell
electrons and nuclei. The long end of the EUV spectrum is set by a
prominent He+ spectral line at 30.4 nm. EUV is strongly absorbed
by most known materials, but it is possible to synthesize multilayer
optics that reflect up to about 50 percent of EUV radiation at normal
incidence. This technology was pioneered by the
NIXT and MSSTA
sounding rockets in the 1990s, and it has been used to make telescopes
for solar imaging. See also the
Extreme Ultraviolet Explorer
Extreme Ultraviolet Explorer (EUVE)
Levels of ozone at various altitudes and blocking of different bands
of ultraviolet radiation. In essence, all UVC is blocked by diatomic
oxygen (100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in
the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA
is hardly affected by ozone, and most of it reaches the ground. UVA
makes up almost all of the circa 25 percent of the Sun's total UV
light that penetrates the Earth's atmosphere.
Very hot objects emit UV radiation (see black-body radiation). The Sun
emits ultraviolet radiation at all wavelengths, including the extreme
ultraviolet where it crosses into X-rays at 10 nm. Extremely hot
stars emit proportionally more UV radiation than the Sun.
space at the top of
Earth's atmosphere (see solar constant) is
composed of about 50% infrared light, 40% visible light, and 10%
ultraviolet light, for a total intensity of about 1400 W/m2 in
However, at ground level sunlight is 44% visible light, 3% ultraviolet
Sun at its zenith), and the remainder infrared.
Thus, the atmosphere blocks about 77% of the Sun's UV, almost entirely
in the shorter UV wavelengths, when the
Sun is highest in the sky
(zenith). Of the ultraviolet radiation that reaches the Earth's
surface, more than 95% is the longer wavelengths of UVA, with the
small remainder UVB. There is essentially no UVC. The fraction of
UVB which remains in UV radiation after passing through the atmosphere
is heavily dependent on cloud cover and atmospheric conditions. Thick
clouds block UVB effectively, but in "partly cloudy" days, patches of
blue sky showing between clouds are also sources of (scattered) UVA
and UVB, which are produced by
Rayleigh scattering in the same way as
the visible blue light from those parts of the sky.
UV-B also plays a
major role in plant development as it affects most of the plant
The shorter bands of UVC, as well as even more-energetic UV radiation
produced by the Sun, are absorbed by oxygen and generate the ozone in
the ozone layer when single oxygen atoms produced by UV photolysis of
dioxygen react with more dioxygen. The ozone layer is especially
important in blocking most UVB and the remaining part of UVC not
already blocked by ordinary oxygen in air.
Blockers and absorbers
Ultraviolet absorbers are molecules used in organic materials
(polymers, paints, etc.) to absorb UV radiation to reduce the UV
degradation (photo-oxidation) of a material. The absorbers can
themselves degrade over time, so monitoring of absorber levels in
weathered materials is necessary.
In sunscreen, ingredients that absorb UVA/UVB rays, such as
avobenzone, oxybenzone and octyl methoxycinnamate, are organic
chemical absorbers or "blockers". They are contrasted with inorganic
absorbers/"blockers" of UV radiation such as carbon black, titanium
dioxide and zinc oxide.
For clothing, the
Ultraviolet Protection Factor (UPF) represents the
ratio of sunburn-causing UV without and with the protection of the
fabric, similar to SPF (
Sun Protection Factor) ratings for sunscreen.
Standard summer fabrics have UPF of approximately 6, which means that
about 20% of UV will pass through.
Suspended nanoparticles in stained glass prevent UV rays from causing
chemical reactions that change image colors. A set of stained glass
color reference chips is planned to be used to calibrate the color
cameras for the 2019
ESA Mars rover mission, since they will remain
unfaded by the high level of UV present at the surface of Mars.
Common soda lime glass is partially transparent to UVA but is opaque
to shorter wavelengths, whereas fused quartz glass, depending on
quality, can be transparent even to vacuum UV wavelengths. Ordinary
window glass passes about 90% of the light above 350 nm, but
blocks over 90% of the light below 300 nm.
Wood's glass is a nickel-bearing form of glass with a deep blue-purple
color that blocks most visible light and passes ultraviolet.
Two black light fluorescent tubes, showing use. The longer tube is a
F15T8/BLB 18 inch, 15 watt tube, shown in the bottom image in a
standard plug-in fluorescent fixture. The shorter is an F8T5/BLB 12
inch, 8 watt tube, used in a portable battery-powered black light sold
as a pet urine detector.
Main article: Blacklight
A black light lamp emits long-wave UVA radiation and little visible
light. Fluorescent black light lamps work similarly to other
fluorescent lamps, but use a phosphor on the inner tube surface which
emits UVA radiation instead of visible light. Some lamps use a
Wood's glass optical filter that blocks almost all
visible light with wavelengths longer than 400 nanometres. Others
use plain glass instead of the more expensive Wood's glass, so they
appear light-blue to the eye when operating. A black light may also be
formed, very inefficiently, by using a layer of
Wood's glass in the
envelope for an incandescent bulb. Though cheaper than fluorescent UV
lamps, only 0.1% of the input power is emitted as usable ultraviolet
radiation. Mercury-vapor black lights in ratings up to 1 kW with
UV-emitting phosphor and an envelope of
Wood's glass are used for
theatrical and concert displays. Black lights are used in applications
in which extraneous visible light must be minimized; mainly to observe
fluorescence, the colored glow that many substances give off when
exposed to UV light. UVA/UVB emitting bulbs are also sold for other
special purposes, such as tanning lamps and reptile-keeping.
Short-wave ultraviolet lamps
9-watt germicidal UV lamp, in compact fluorescent (CF) form factor
Commercial germicidal lamp in butcher shop
UV lamps are made using a lamp tube with no phosphor coating
composed of fused quartz, since ordinary glass absorbs UVC. These
lamps emit ultraviolet light with two peaks in the UVC band at
253.7 nm and 185 nm due to the mercury within the lamp, as
well as some visible light. From 85% to 90% of the UV produced by
these lamps is at 253.7 nm, whereas only 5–10% is at
185 nm. The fused quartz glass tube passes the
253 nm radiation but blocks the 185 nm wavelength. Such
tubes have two or three times the UVC power of a regular fluorescent
lamp tube. These low-pressure lamps have a typical efficiency of
approximately 30–40%, meaning that for every 100 watts of
electricity consumed by the lamp, they will produce approximately
30–40 watts of total UV output. These "germicidal" lamps are used
extensively for disinfection of surfaces in laboratories and
food-processing industries, and for disinfecting water supplies.
Halogen lamps with fused quartz envelopes are used as inexpensive UV
light sources in the near UV range, from 400 to 300 nm, in some
Main article: Gas-discharge lamp
Specialized UV gas-discharge lamps containing different gases produce
UV radiation at particular spectral lines for scientific purposes.
Argon and deuterium arc lamps are often used as stable sources, either
windowless or with various windows such as magnesium fluoride.
These are often the emitting sources in UV spectroscopy equipment for
Other UV sources with more continuous emission spectra include xenon
arc lamps (commonly used as sunlight simulators), deuterium arc lamps,
mercury-xenon arc lamps, and metal-halide arc lamps.
The excimer lamp, a UV source developed within the last two decades,
is seeing increasing use in scientific fields. It has the advantages
of high-intensity, high efficiency, and operation at a variety of
wavelength bands into the vacuum ultraviolet.
A 380 nanometre UV
LED makes some common household items fluoresce.
Light-emitting diodes (LEDs) can be manufactured to emit radiation in
the ultraviolet range.
LED efficiency at 365 nm is about 5–8%,
whereas efficiency at 395 nm is closer to 20%, and power outputs
at these longer UV wavelengths are also better. Such
LED arrays are
beginning to be used for
UV curing applications, and are already
successful in digital print applications and inert UV curing
environments. Power densities approaching 3 W/cm2 (30 kW/m2)
are now possible, and this, coupled with recent developments by
photoinitiator and resin formulators, makes the expansion of LED-cured
UV materials likely.
UVC LEDs are beginning to be used in disinfection and as line
sources to replace deuterium lamps in liquid chromatography
Gas lasers, laser diodes and solid-state lasers can be manufactured to
emit ultraviolet rays, and lasers are available which cover the entire
UV range. The nitrogen gas laser uses electronic excitation of
nitrogen molecules to emit a beam that is mostly UV. The strongest
ultraviolet lines are at 337.1 nm and 357.6.6 nm,
wavelength. Another type of high power gas laser is the excimer laser.
They are widely used lasers emitting in ultraviolet and vacuum
ultraviolet wavelength ranges. Presently, UV argon-fluoride (ArF)
excimer lasers operating at 193 nm are routinely used in
integrated circuit production by photolithography. The current
wavelength limit of production of coherent UV is about 126 nm,
characteristic of the Ar2* excimer laser.
Direct UV-emitting laser diodes are available at 375 nm. UV
diode lasers have been demonstrated using Ce:LiSAF crystals
(cerium-doped lithium strontium aluminum fluoride), a process
developed in the 1990s at Lawrence Livermore National Laboratory.
Wavelengths shorter than 325 nm are commercially generated in
diode-pumped solid-state lasers.
Ultraviolet lasers can also be made
by applying frequency conversion to lower-frequency lasers.
Ultraviolet lasers have applications in industry (laser engraving),
medicine (dermatology, and keratectomy), chemistry (MALDI), free air
secure communications, computing (optical storage) and manufacture of
Tunable vacuum ultraviolet (VUV) via sum and difference frequency
The vacuum ultraviolet (VUV) band (100–200 nm) can be generated
by non-linear 4 wave mixing in gases by sum or difference frequency
mixing of 2 or more longer wavelength lasers. The generation is
generally done in gasses (e.g. krypton, hydrogen which are two-photon
resonant near 193 nm) or metal vapors (e.g. magnesium). By
making one of the lasers tunable, the VUV can be tuned. If one of the
lasers is resonant with a transition in the gas or vapor then the VUV
production is intensified. However, resonances also generate
wavelength dispersion, and thus the phase matching can limit the
tunable range of the 4 wave mixing. Difference frequency mixing
(lambda1 + lambda2 − lambda3) has an advantage over sum frequency
mixing because the phase matching can provide greater tuning. In
particular, difference frequency mixing two photons of an ArF
(193 nm) excimer laser with a tunable visible or near IR laser in
hydrogen or krypton provides resonantly enhanced tunable VUV covering
from 100 nm to 200 nm. Practically, the lack of suitable
gas/vapor cell window materials above the lithium fluoride cut-off
wavelength limit the tuning range to longer than about 110 nm.
Tunable VUV wavelengths down to 75 nm was achieved using
window-free configurations. 
Plasma and synchrotron sources of extreme UV
Lasers have been used to indirectly generate non-coherent extreme UV
(EUV) radiation at 13.5 nm for extreme ultraviolet lithography.
The EUV is not emitted by the laser, but rather by electron
transitions in an extremely hot tin or xenon plasma, which is excited
by an excimer laser. This technique does not require a
synchrotron, yet can produce UV at the edge of the
Synchrotron light sources can also produce all wavelengths of UV,
including those at the boundary of the UV and
X-ray spectra at
Human health-related effects
Further information: Health effects of sun exposure
The impact of ultraviolet radiation on human health has implications
for the risks and benefits of sun exposure and is also implicated in
issues such as fluorescent lamps and health. Getting too much sun
exposure can be harmful, but in moderation is beneficial.
UV light causes the body to produce vitamin D, which is essential for
life. The human body needs some UV radiation in order for one to
maintain adequate vitamin D levels; however, the harmful effects
typically outweigh the benefits.
Exposure to ultraviolet radiation from the sun is a source of vitamin
D. One minimal erythemal dose of sunlight UV radiation provides the
equivalent of about 20,000 IU of vitamin D2, taken as an oral
supplement. If an adult's arms and legs are exposed
to a half minimal erythemal UV radiation, it is the same as taking
3,000 IU of vitamin D3 through an oral supplement. This exposure of
10–15 minutes, on a frequency of two to three times per week will
cause the adult's skin to produce enough vitamin D. It is not
necessary to expose the face to the UV, as facial skin provides little
vitamin D3. Individuals whose metabolism makes taking oral vitamin D
ineffective are able, through exposure to an ultraviolet lamp that
UV-B radiation, to achieve a 25 (OH) D blood level.
Three benefits of UV exposure are production of vitamin D, improvement
in mood, and increased energy.
UVB induces production of vitamin D in the skin at rates of up to
1,000 IUs per minute. This vitamin helps to regulate calcium
metabolism (vital for the nervous system and bone health), immunity,
cell proliferation, insulin secretion, and blood pressure. In
third-world countries, foods fortified with vitamin D are "practically
nonexistent." Most people in the world depend on the sun to get
There are not many foods that naturally have vitamin D. Examples
are cod liver oil and oily fish. If people cannot get sunlight, then
they will need 1,000 IU of vitamin D per day to stay healthy. A
person would have to eat oily fish three or four times per week in
order to get enough vitamin D from that food source alone.
People with higher levels of vitamin D tend to have lower rates of
diabetes, heart disease, and stroke and tend to have lower blood
pressure. However, it has been found that vitamin D supplementation
does not improve cardiovascular health or metabolism, so the link with
vitamin D must be in part indirect. People who get
more sun are generally healthier, and also have higher vitamin D
levels. It has been found that ultraviolet radiation (even UVA)
produces nitric oxide (NO) in the skin, and nitric oxide can lower
blood pressure. High blood pressure increases the risk of stroke and
heart disease. Although long-term exposure to ultraviolet contributes
to non-melanoma skin cancers that are rarely fatal, it has been found
in a Danish study that those who get these cancers were less likely to
die during the study, and were much less likely to have a heart
attack, than those who did not have these cancers.
People in certain situations, such as people with intellectual
disabilities and neurodevelopmental disorders who stay inside most of
the time have low vitamin D levels. Getting enough vitamin D can help
stave off "autoimmune diseases, cardiovascular disease, many types of
cancer, dementia, types 1 and 2 diabetes mellitus, and respiratory
Fetuses and children who do not get enough vitamin D can suffer from
"growth retardation and skeletal deformities."
UV rays also treat certain skin conditions. Modern phototherapy has
been used to successfully treat psoriasis, eczema, jaundice, vitiligo,
atopic dermatitis, and localized scleroderma. In addition, UV
light, in particular UVB radiation, has been shown to induce cell
cycle arrest in keratinocytes, the most common type of skin cell.
As such, sunlight therapy can be a candidate for treatment of
conditions such as psoriasis and exfoliative cheilitis, conditions in
which skin cells divide more rapidly than usual or necessary.
Cardiovascular and hypertension
Worldwide, one billion people suffer from hypertension. In the U.S.,
half of the 146 million hypertensive patients don't have their blood
pressure under control. In hypertension patients who suffer from
vitamin D deficiency, UVB radiation (but not UVA) lowered blood
Modern pharmaceutical therapy has resulted in an overall reduction in
hypertension, particularly in countries with high GDP per capita. A
review of blood pressure statistics before these pharmaceuticals were
available shows a coherent correlation between high blood pressure and
higher latitude. Seasons of the year also impact high blood pressure;
BP is lower in the summer months in high latitudes than it is in the
winter, when there is less sunlight. Individuals with more sun
exposure synthesize more active vitamin D (1,25 di-hydroxy
cholecalciferol) from diet or ultraviolet radiation exposure. A
combination of lower ultraviolet radiation with insufficient vitamin D
in a diet leads to vitamin D deficiency. Individuals whose vitamin D
ranks in the lowest quartile have double the all-cause mortality of
those who rank in the highest quartile. They are also more likely to
suffer from cardiovascular disease, hypertension and organ
Medical trials have demonstrated that vitamin D supplements do not
prevent or treat hypertension or cardiovascular disease, although they
can help in skeletal metabolism. Epidemiological and observational
studies show indications that exposure to ultraviolet radiation,
particularly sunlight, might reduce all-cause mortality and can help
reduce cardiovascular disease and hypertension. One hundred years of
scientific data has demonstrated that the effect of ultraviolet
radiation on human skin is carcinogenic. There is a lack of evidence
that this carcinogenic effect, like risks such as smoking or alcohol,
is responsible for higher mortality. There are significant archives of
studies demonstrating that ultraviolet radiation from sunlight
provides measurable health benefits, independent of vitamin D.
Vitamin D promotes the creation of serotonin. The production of
serotonin is in direct proportion to the degree of bright sunlight the
body receives. Conversely, serotonin levels decrease when sunlight is
at its lowest levels, as in autumn and winter.
Changes in serotonin levels affect how humans act relative to mood and
behavior. Measured serotonin is much higher among those who die in
summer, rather than winter.
Serotonin is a monoamine neurotransmitter that is thought to provide
sensations of happiness, well being and serenity to human beings.
It is thought that serotonin affects a wide range of human bodily
functions from anxiety and mood to bowel function to bone density to
sexuality. Its importance in human activity continues to be a source
of much scientific examination and experimentation.
The amount of the brown pigment melanin in the skin increases after
exposure to UV radiation at moderate levels depending on skin type;
this is commonly known as a sun tan.
Melanin is an excellent
photoprotectant that absorbs both UVB and UVA radiation and dissipates
the energy as harmless heat, protecting the skin against both direct
"There is no doubt that a little sunlight is good for you! But 5 to 15
minutes of casual sun exposure of hands, face and arms two to three
times a week during the summer months is sufficient to keep your
vitamin D levels high." – World Health Organization
Ultraviolet light and cancer
In humans, excessive exposure to UV radiation can result in acute and
chronic harmful effects on the eye's dioptric system and retina. The
risk is elevated at high altitudes and people living in high latitude
countries where snow covers the ground right into early summer and sun
positions even at zenith are low, are particularly at risk. Skin,
the circadian and immune systems can also be affected.
Ultraviolet photons harm the
DNA molecules of living organisms in
different ways. In one common damage event, adjacent thymine bases
bond with each other, instead of across the "ladder". This "thymine
dimer" makes a bulge, and the distorted
DNA molecule does not function
Sunburn effect (as measured by the UV Index) is the product of the
sunlight spectrum (radiation intensity) and the erythemal action
spectrum (skin sensitivity) across the range of UV wavelengths.
Sunburn production per milliwatt is increased by almost a factor of
100 between the near UVB wavelengths of 315–295 nm
The differential effects of various wavelengths of light on the human
cornea and skin are sometimes called the "erythemal action
spectrum.". The action spectrum shows that UVA does not cause
immediate reaction, but rather UV begins to cause photokeratitis and
skin redness (with Caucasians more sensitive) at wavelengths starting
near the beginning of the UVB band at 315 nm, and rapidly
increasing to 300 nm. The skin and eyes are most sensitive to
damage by UV at 265–275 nm, which is in the lower UVC band. At
still shorter wavelengths of UV, damage continues to happen, but the
overt effects are not as great with so little penetrating the
atmosphere. The WHO-standard ultraviolet index is a widely publicized
measurement of total strength of UV wavelengths that cause sunburn on
human skin, by weighting UV exposure for action spectrum effects at a
given time and location. This standard shows that most sunburn happens
due to UV at wavelengths near the boundary of the UVA and UVB bands.
Bioolympics discover UV reaction index to detect the leak of UV light.
Overexposure to UVB radiation not only can cause sunburn but also some
forms of skin cancer. However, the degree of redness and eye
irritation (which are largely not caused by UVA) do not predict the
long-term effects of UV, although they do mirror the direct damage of
DNA by ultraviolet.
All bands of UV radiation damage collagen fibers and accelerate aging
of the skin. Both UVA and UVB destroy vitamin A in skin, which may
cause further damage.
UVB radiation can cause direct
DNA damage. This cancer connection
is one reason for concern about ozone depletion and the ozone hole.
The most deadly form of skin cancer, malignant melanoma, is mostly
DNA damage independent from UVA radiation. This can be seen
from the absence of a direct UV signature mutation in 92% of all
melanoma. Occasional overexposure and sunburn are probably greater
risk factors for melanoma than long-term moderate exposure. UVC is
the highest-energy, most-dangerous type of ultraviolet radiation, and
causes adverse effects that can variously be mutagenic or
In the past, UVA was considered not harmful or less harmful than UVB,
but today it is known to contribute to skin cancer via indirect DNA
damage (free radicals such as reactive oxygen species). UVA can
generate highly reactive chemical intermediates, such as hydroxyl and
oxygen radicals, which in turn can damage DNA. The
DNA damage caused
indirectly to skin by UVA consists mostly of single-strand breaks in
DNA, while the damage caused by UVB includes direct formation of
thymine dimers or other pyrimidine dimers and double-strand DNA
breakage. UVA is immunosuppressive for the entire body (accounting
for a large part of the immunosuppressive effects of sunlight
exposure), and is mutagenic for basal cell keratinocytes in skin.
UVB photons can cause direct
DNA damage. UVB radiation excites DNA
molecules in skin cells, causing aberrant covalent bonds to form
between adjacent pyrimidine bases, producing a dimer. Most UV-induced
pyrimidine dimers in
DNA are removed by the process known as
nucleotide excision repair that employs about 30 different
proteins. Those pyrimidine dimers that escape this repair process
can induce a form of programmed cell death (apoptosis) or can cause
DNA replication errors leading to mutation.
As a defense against UV radiation, the amount of the brown pigment
melanin in the skin increases when exposed to moderate (depending on
skin type) levels of radiation; this is commonly known as a sun tan.
The purpose of melanin is to absorb UV radiation and dissipate the
energy as harmless heat, blocking the UV from damaging skin tissue.
UVA gives a quick tan that lasts for days by oxidizing melanin that
was already present and triggers the release of the melanin from
melanocytes. UVB yields a tan that takes roughly 2 days to develop
because it stimulates the body to produce more melanin.
Sunscreen prevents the direct
DNA damage which causes sunburn. Most of
these products contain an SPF rating to show how well they block UVB
rays. The SPF rating, however, offers no data about UVA protection.
Some sunscreen lotions now include compounds such as titanium dioxide
which helps protect against UVA rays. Other UVA blocking compounds
found in sunscreen include zinc oxide and avobenzone.
Sunscreen safety debate
Main article: Sunscreen
Demonstration of the effect of sunscreen. The man's face has sunscreen
on his right only. The left image is a regular photograph of the face;
the right image is taken by reflected UV light. The side of the face
with sunscreen is darker because the sunscreen absorbs the UV light.
Medical organizations recommend that patients protect themselves from
UV radiation by using sunscreen. Five sunscreen ingredients have been
shown to protect mice against skin tumors. However, some sunscreen
chemicals produce potentially harmful substances if they are
illuminated while in contact with living cells. The amount of
sunscreen that penetrates into the lower layers of the skin may be
large enough to cause damage.
Sunscreen reduces the direct
DNA damage that causes sunburn, by
blocking UVB, and the usual SPF rating indicates how effectively this
radiation is blocked. SPF is, therefore, also called UVB-PF, for "UVB
protection factor". This rating, however, offers no data about
important protection against UVA, which does not primarily cause
sunburn but is still harmful, since it causes indirect
DNA damage and
is also considered carcinogenic. Several studies suggest that the
absence of UVA filters may be the cause of the higher incidence of
melanoma found in sunscreen users compared to
The photochemical properties of melanin make it an excellent
photoprotectant. However, sunscreen chemicals cannot dissipate the
energy of the excited state as efficiently as melanin and therefore,
if sunscreen ingredients penetrate into the lower layers of the skin,
the amount of reactive oxygen species may be
increased. The amount of sunscreen that penetrates
through the stratum corneum may or may not be large enough to cause
In an experiment by Hanson et al. that was published in 2006, the
amount of harmful reactive oxygen species (ROS) was measured in
untreated and in sunscreen treated skin. In the first 20 minutes, the
film of sunscreen had a protective effect and the number of ROS
species was smaller. After 60 minutes, however, the amount of absorbed
sunscreen was so high that the amount of ROS was higher in the
sunscreen-treated skin than in the untreated skin. The study
indicates that sunscreen must be reapplied within 2 hours in order to
prevent UV light from penetrating to sunscreen-infused live skin
Aggravation of certain skin conditions
Ultraviolet radiation can aggravate several skin conditions and
Systemic lupus erythematosus
Sinear Usher syndrome
Signs are often used to warn of the hazard of strong UV sources.
The eye is most sensitive to damage by UV in the lower UVC band at
Radiation of this wavelength is almost absent from
sunlight but is found in welder's arc lights and other artificial
sources. Exposure to these can cause "welder's flash" or "arc eye"
(photokeratitis) and can lead to cataracts, pterygium and pinguecula
formation. To a lesser extent, UVB in sunlight from 310–280 nm
also causes photokeratitis ("snow blindness"), and the cornea, the
lens, and the retina can be damaged.
Protective eyewear is beneficial to those exposed to ultraviolet
radiation. Since light can reach the eyes from the sides,
full-coverage eye protection is usually warranted if there is an
increased risk of exposure, as in high-altitude mountaineering.
Mountaineers are exposed to higher-than-ordinary levels of UV
radiation, both because there is less atmospheric filtering and
because of reflection from snow and ice. Ordinary, untreated
eyeglasses give some protection. Most plastic lenses give more
protection than glass lenses, because, as noted above, glass is
transparent to UVA and the common acrylic plastic used for lenses is
less so. Some plastic lens materials, such as polycarbonate,
inherently block most UV.
Degradation of polymers, pigments and dyes
Main article: UV degradation
UV damaged polypropylene rope (left) and new rope (right)
UV degradation is one form of polymer degradation that affects
plastics exposed to sunlight. The problem appears as discoloration or
fading, cracking, loss of strength or disintegration. The effects of
attack increase with exposure time and sunlight intensity. The
addition of UV absorbers inhibits the effect.
Sensitive polymers include thermoplastics and speciality fibers like
aramids. UV absorption leads to chain degradation and loss of strength
at sensitive points in the chain structure.
Aramid rope must be
shielded with a sheath of thermoplastic if it is to retain its
IR spectrum showing carbonyl absorption due to
UV degradation of
Many pigments and dyes absorb UV and change colour, so paintings and
textiles may need extra protection both from sunlight and fluorescent
bulbs, two common sources of UV radiation. Window glass absorbs some
harmful UV, but valuable artifacts need extra shielding. Many museums
place black curtains over watercolour paintings and ancient textiles,
for example. Since watercolours can have very low pigment levels, they
need extra protection from UV. Various forms of picture framing glass,
including acrylics (plexiglass), laminates, and coatings, offer
different degrees of UV (and visible light) protection.
Because of its ability to cause chemical reactions and excite
fluorescence in materials, ultraviolet radiation has a number of
applications. The following table gives some uses of specific
wavelength bands in the UV spectrum
Extreme ultraviolet lithography
30–200 nm: Photoionization, ultraviolet photoelectron
spectroscopy, standard integrated circuit manufacture by
230–365 nm: UV-ID, label tracking, barcodes
230–400 nm: Optical sensors, various instrumentation
240–280 nm: Disinfection, decontamination of surfaces and water
DNA absorption has a peak at 260 nm)
200–400 nm: Forensic analysis, drug detection
DNA sequencing, drug discovery
Medical imaging of cells
Light therapy in medicine
300–365 nm: Curing of polymers and printer inks
350–370 nm: Bug zappers (flies are most attracted to light at
A portrait taken using only UV light between the wavelengths of 335
and 365 nanometers.
Photographic film responds to ultraviolet radiation but the glass
lenses of cameras usually block radiation shorter than 350 nm.
Slightly yellow UV-blocking filters are often used for outdoor
photography to prevent unwanted bluing and overexposure by UV rays.
For photography in the near UV, special filters may be used.
Photography with wavelengths shorter than 350 nm requires special
quartz lenses which do not absorb the radiation. Digital cameras
sensors may have internal filters that block UV to improve color
rendition accuracy. Sometimes these internal filters can be removed,
or they may be absent, and an external visible-light filter prepares
the camera for near-UV photography. A few cameras are designed for use
in the UV.
Photography by reflected ultraviolet radiation is useful for medical,
scientific, and forensic investigations, in applications as widespread
as detecting bruising of skin, alterations of documents, or
restoration work on paintings. Photography of the fluorescence
produced by ultraviolet illumination uses visible wavelengths of
Aurora at Jupiter's north pole as seen in ultraviolet light by the
Hubble Space Telescope.
In ultraviolet astronomy, measurements are used to discern the
chemical composition of the interstellar medium, and the temperature
and composition of stars. Because the ozone layer blocks many UV
frequencies from reaching telescopes on the surface of the Earth, most
UV observations are made from space.
Electrical and electronics industry
Corona discharge on electrical apparatus can be detected by its
ultraviolet emissions. Corona causes degradation of electrical
insulation and emission of ozone and nitrogen oxide.
EPROMs (Erasable Programmable Read-Only Memory) are erased by exposure
to UV radiation. These modules have a transparent (quartz) window on
the top of the chip that allows the UV radiation in.
Fluorescent dye uses
Colorless fluorescent dyes that emit blue light under UV are added as
optical brighteners to paper and fabrics. The blue light emitted by
these agents counteracts yellow tints that may be present and causes
the colors and whites to appear whiter or more brightly colored.
UV fluorescent dyes that glow in the primary colors are used in
paints, papers, and textiles either to enhance color under daylight
illumination or to provide special effects when lit with UV lamps.
Blacklight paints that contain dyes that glow under UV are used in a
number of art and esthetic applications.
A bird appears on many Visa credit cards when they are held under a UV
To help prevent counterfeiting of currency, or forgery of important
documents such as driver's licenses and passports, the paper may
include a UV watermark or fluorescent multicolor fibers that are
visible under ultraviolet light. Postage stamps are tagged with a
phosphor that glows under UV rays to permit automatic detection of the
stamp and facing of the letter.
UV fluorescent dyes are used in many applications (for example,
biochemistry and forensics). Some brands of pepper spray will leave an
invisible chemical (UV dye) that is not easily washed off on a
pepper-sprayed attacker, which would help police identify the attacker
In some types of nondestructive testing UV stimulates fluorescent dyes
to highlight defects in a broad range of materials. These dyes may be
carried into surface-breaking defects by capillary action (liquid
penetrant inspection) or they may be bound to ferrite particles caught
in magnetic leakage fields in ferrous materials (magnetic particle
UV is an investigative tool at the crime scene helpful in locating and
identifying bodily fluids such as semen, blood, and saliva. For
example, ejaculated fluids or saliva can be detected by high-power UV
sources, irrespective of the structure or colour of the surface the
fluid is deposited upon. UV-Vis microspectroscopy is also used to
analyze trace evidence, such as textile fibers and paint chips, as
well as questioned documents.
Other applications include the authentication of various collectibles
and art, and detecting counterfeit currency. Even materials not
specially marked with UV sensitive dyes may have distinctive
fluorescence under UV exposure or may fluoresce differently under
short-wave versus long-wave ultraviolet.
Enhancing contrast of ink
Using multi-spectral imaging it is possible to read illegible papyrus,
such as the burned papyri of the
Villa of the Papyri
Villa of the Papyri or of
Oxyrhynchus, or the Archimedes palimpsest. The technique involves
taking pictures of the illegible document using different filters in
the infrared or ultraviolet range, finely tuned to capture certain
wavelengths of light. Thus, the optimum spectral portion can be found
for distinguishing ink from paper on the papyrus surface.
Simple NUV sources can be used to highlight faded iron-based ink on
After a training exercise involving fake body fluids, a healthcare
worker's personal protective equipment is checked with ultraviolet
light to find invisible drops of fluids. These fluids could contain
deadly viruses or other contamination.
Ultraviolet aids in the detection of organic material deposits that
remain on surfaces where periodic cleaning and sanitizing may not have
been properly accomplished. It is used in the hotel industry,
manufacturing, and other industries where levels of cleanliness or
contamination are inspected.
Perennial news feature for many television news organizations involves
an investigative reporter's using a similar device to reveal
unsanitary conditions in hotels, public toilets, hand rails, and
UV/VIS spectroscopy is widely used as a technique in chemistry to
analyze chemical structure, the most notable one being conjugated
systems. UV radiation is often used to excite a given sample where the
fluorescent emission is measured with a spectrofluorometer. In
biological research, UV radiation is used for quantification of
nucleic acids or proteins.
A collection of mineral samples brilliantly fluorescing at various
wavelengths as seen while being irradiated by UV light.
Ultraviolet lamps are also used in analyzing minerals and gems.
In pollution control applications, ultraviolet analyzers are used to
detect emissions of nitrogen oxides, sulfur compounds, mercury, and
ammonia, for example in the flue gas of fossil-fired power
Ultraviolet radiation can detect thin sheens of spilled
oil on water, either by the high reflectivity of oil films at UV
wavelengths, fluorescence of compounds in oil or by absorbing of UV
Raman scattering in water.
Material science uses
See also: Flame detector
In general, ultraviolet detectors use either a solid-state device,
such as one based on silicon carbide or aluminium nitride, or a
gas-filled tube as the sensing element. UV detectors that are
sensitive to UV in any part of the spectrum respond to irradiation by
sunlight and artificial light. A burning hydrogen flame, for instance,
radiates strongly in the 185- to 260-nanometer range and only very
weakly in the IR region, whereas a coal fire emits very weakly in the
V band yet very strongly at IR wavelengths; thus, a fire detector
that operates using both UV and IR detectors is more reliable than one
with a UV detector alone. Virtually all fires emit some radiation in
the UVC band, whereas the Sun's radiation at this band is absorbed by
the Earth's atmosphere. The result is that the UV detector is "solar
blind", meaning it will not cause an alarm in response to radiation
from the Sun, so it can easily be used both indoors and outdoors.
UV detectors are sensitive to most fires, including hydrocarbons,
metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding,
electrical arcs, lightning, X-rays used in nondestructive metal
testing equipment (though this is highly unlikely), and radioactive
materials can produce levels that will activate a UV detection system.
The presence of UV-absorbing gases and vapors will attenuate the UV
radiation from a fire, adversely affecting the ability of the detector
to detect flames. Likewise, the presence of an oil mist in the air or
an oil film on the detector window will have the same effect.
Ultraviolet radiation is used for very fine resolution
photolithography, a procedure wherein a chemical called a photoresist
is exposed to UV radiation that has passed through a mask. The
exposure causes chemical reactions to occur in the photoresist. After
removal of unwanted photoresist, a pattern determined by the mask
remains on the sample. Steps may then be taken to "etch" away, deposit
on or otherwise modify areas of the sample where no photoresist
Photolithography is used in the manufacture of semiconductors,
integrated circuit components, and printed circuit boards.
Photolithography processes used to fabricate electronic integrated
circuits presently use 193 nm UV and are experimentally using
13.5 nm UV for extreme ultraviolet lithography.
Electronic components that require clear transparency for light to
exit or enter (photovoltaic panels and sensors) can be potted using
acrylic resins that are cured using UV energy. The advantages are low
VOC emissions and rapid curing.
Effects of UV on finished surfaces in 0, 20 and 43 hours.
Certain inks, coatings, and adhesives are formulated with
photoinitiators and resins. When exposed to UV light, polymerization
occurs, and so the adhesives harden or cure, usually within a few
seconds. Applications include glass and plastic bonding, optical fiber
coatings, the coating of flooring,
UV coating and paper finishes in
offset printing, dental fillings, and decorative fingernail "gels".
UV sources for
UV curing applications include UV lamps, UV LEDs, and
Excimer flash lamps. Fast processes such as flexo or offset printing
require high-intensity light focused via reflectors onto a moving
substrate and medium so high-pressure Hg (mercury) or Fe (iron,
doped)-based bulbs are used, energized with electric arcs or
microwaves. Lower-power fluorescent lamps and LEDs can be used for
static applications. Small high-pressure lamps can have light focused
and transmitted to the work area via liquid-filled or fiber-optic
The impact of UV on polymers is used for modification of the
(roughness and hydrophobicity) of polymer surfaces. For example, a
poly(methyl methacrylate) surface can be smoothed by vacuum
UV radiation is useful in preparing low-surface-energy polymers for
Polymers exposed to UV will oxidize, thus raising the
surface energy of the polymer. Once the surface energy of the polymer
has been raised, the bond between the adhesive and the polymer is
Using a catalytic chemical reaction from titanium dioxide and UVC
exposure, oxidation of organic matter converts pathogens, pollens, and
mold spores into harmless inert byproducts. The cleansing mechanism of
UV is a photochemical process. Contaminants in the indoor environment
are almost entirely organic carbon-based compounds, which break down
when exposed to high-intensity UV at 240 to 280 nm. Short-wave
ultraviolet radiation can destroy
DNA in living microorganisms.
UVC's effectiveness is directly related to intensity and exposure
UV has also been shown to reduce gaseous contaminants such as carbon
monoxide and VOCs.
UV lamps radiating at 184 and
254 nm can remove low concentrations of hydrocarbons and carbon
monoxide if the air is recycled between the room and the lamp chamber.
This arrangement prevents the introduction of ozone into the treated
air. Likewise, air may be treated by passing by a single UV source
operating at 184 nm and passed over iron pentaoxide to remove the
ozone produced by the UV lamp.
Sterilization and disinfection
Ultraviolet germicidal irradiation
A low-pressure mercury vapor discharge tube floods the inside of a
hood with shortwave UV light when not in use, sterilizing
microbiological contaminants from irradiated surfaces.
Ultraviolet lamps are used to sterilize workspaces and tools used in
biology laboratories and medical facilities. Commercially available
low-pressure mercury-vapor lamps emit about 86% of their radiation at
254 nanometers (nm), with 265 nm being the peak germicidal
effectiveness curve. UV at these germicidal wavelengths damage a
DNA so that it cannot reproduce, making it harmless,
(even though the organism may not be killed). Since microorganisms can
be shielded from ultraviolet rays in small cracks and other shaded
areas, these lamps are used only as a supplement to other
UV-C LEDs are relatively new to the commercial market and are gaining
in popularity. Due to their monochromatic nature (± 5 nm)
these LEDs can target a specific wavelength needed for disinfection.
This is especially important knowing that pathogens vary in their
sensitivity to specific UV wavelengths. LEDs are mercury free, instant
on/off, and have unlimited cycling throughout the day.
Disinfection using UV radiation is commonly used in wastewater
treatment applications and is finding an increased usage in municipal
drinking water treatment. Many bottlers of spring water use UV
disinfection equipment to sterilize their water. Solar water
disinfection has been researched for cheaply treating
contaminated water using natural sunlight. The UV-A irradiation and
increased water temperature kill organisms in the water.
Ultraviolet radiation is used in several food processes to kill
unwanted microorganisms. UV can be used to pasteurize fruit juices by
flowing the juice over a high-intensity ultraviolet source. The
effectiveness of such a process depends on the UV absorbance of the
Pulsed light (PL) is a technique of killing microorganisms on surfaces
using pulses of an intense broad spectrum, rich in UV-C between 200
and 280 nm. Pulsed light works with xenon flash lamps that can produce
flashes several times per second.
Disinfection robots use pulsed
Some animals, including birds, reptiles, and insects such as bees, can
see near-ultraviolet wavelengths. Many fruits, flowers, and seeds
stand out more strongly from the background in ultraviolet wavelengths
as compared to human color vision. Scorpions glow or take on a yellow
to green color under UV illumination, thus assisting in the control of
these arachnids. Many birds have patterns in their plumage that are
invisible at usual wavelengths but observable in ultraviolet, and the
urine and other secretions of some animals, including dogs, cats, and
human beings, are much easier to spot with ultraviolet. Urine trails
of rodents can be detected by pest control technicians for proper
treatment of infested dwellings.
Butterflies use ultraviolet as a communication system for sex
recognition and mating behavior. For example, in the Colias eurytheme
butterfly, males rely on visual cues to locate and identify females.
Instead of using chemical stimuli to find mates, males are attracted
to the ultraviolet-reflecting color of female hind wings. In
Pieris napi butterflies it was shown that females in northern Finland
with less UV-radiation present in the environment possessed stronger
UV signals to attract their males than those occurring further south.
This suggested that it was evolutionarily more difficult to increase
the UV-sensitivity of the eyes of the males than to increae the
UV-signals emitted by the females.
Many insects use the ultraviolet wavelength emissions from celestial
objects as references for flight navigation. A local ultraviolet
emitter will normally disrupt the navigation process and will
eventually attract the flying insect.
Entomologist using a UV light for collecting beetles in Chaco,
The green fluorescent protein (GFP) is often used in genetics as a
marker. Many substances, such as proteins, have significant light
absorption bands in the ultraviolet that are of interest in
biochemistry and related fields. UV-capable spectrophotometers are
common in such laboratories.
Ultraviolet traps called bug zappers are used to eliminate various
small flying insects. They are attracted to the UV and are killed
using an electric shock, or trapped once they come into contact with
the device. Different designs of ultraviolet radiation traps are also
used by entomologists for collecting nocturnal insects during
faunistic survey studies.
Ultraviolet light therapy
Ultraviolet radiation is helpful in the treatment of skin conditions
such as psoriasis and vitiligo. Exposure to UVA, while the skin is
hyper-photosensitive, by taking psoralens is an effective treatment
for psoriasis. Due to the potential of psoralens to cause damage to
PUVA therapy may be used only a limited number of times
over a patient's lifetime.
UVB phototherapy does not require additional medications or topical
preparations for the therapeutic benefit; only the exposure is needed.
However, phototherapy can be effective when used in conjunction with
certain topical treatments such as anthralin, coal tar, and vitamin A
and D derivatives, or systemic treatments such as methotrexate and
Reptiles need UVB for biosynthesis of vitamin D, and other metabolic
processes. Specifically cholecalciferol (vitamin D3), which is needed
to for basic cellular / neural functioning as well as the utilization
calcium for bone and egg production. The UVA wavelength is also
visible to many reptiles and might play a signifiant role in their
ability survive in the wild as well as visual communication between
individuals. Therefore, in a typical reptile enclosure, a fluorescent
UV a/b source (at the proper strength / spectrum for the species),
must be available for many captive species to survive. Simple
supplementation with cholecalciferol (Vitamin D3) will not be enough
as there's a complete biosynthetic pathway that is "leapfrogged"
(risks of possible overdoses), the intermediate molecules and
metabolites also place important functions in the animals health.
Natural sunlight in the right levels is always going to be superior to
artificial sources, but this might be possible for keepers in
different parts of the world.
It is a known problem that high levels of output of the UVa part of
the spectrum can both cause cellular and
DNA damage to sensitive parts
of their bodies - especially the eyes were blindness is the result
from an improper UVa/b source use and placement photokeratitis. For
many keepers there must also be a provision for an adequate heat
source this has resulted in the marketing of heat and light
"combination" products. Keepers should be careful of these
"combination' light/ heat and UVa/b generators, they typically emit
high levels of UVa with lower levels of UVb that are set and difficult
to control so that animals can have their needs met. A better strategy
is to use individual sources of these elements and so they can be
placed and controlled by the keepers for the max benefit of the
The evolution of early reproductive proteins and enzymes is attributed
in modern models of evolutionary theory to ultraviolet radiation. UVB
causes thymine base pairs next to each other in genetic sequences to
bond together into thymine dimers, a disruption in the strand that
reproductive enzymes cannot copy. This leads to frameshifting during
genetic replication and protein synthesis, usually killing the cell.
Before formation of the UV-blocking ozone layer, when early
prokaryotes approached the surface of the ocean, they almost
invariably died out. The few that survived had developed enzymes that
monitored the genetic material and removed thymine dimers by
nucleotide excision repair enzymes. Many enzymes and proteins involved
in modern mitosis and meiosis are similar to repair enzymes, and are
believed to be evolved modifications of the enzymes originally used to
DNA damages caused by UV.
High-energy visible light
UV stabilizers in plastics
Weather testing of polymers
Ultraviolet germicidal irradiation
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